Carl a



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witnesses MW 5M W w U55 nelerence LAiZ-innm C. A. PFANSTIEHL.

PROCESS FOR CLEANING CONTACT POINTS.

APPLICATION FILED JULY 11.1914.

Patented May 27, 1919.

6 ZZ Z.

HHlll Inventor cm A. rrnnsrrniin, orwauxnom, ILLm'oIs,

- NEW YORK.

a s e rnocrfss Eon CLEANING coNTAcT-romrs. 1,304,803. Specification Letters I'atent. Patented May 27, 1919.

' 1914. 'Seria1No.850,350. 3

PATENT. F C -f ASSIGNOR, BY ASSIGNLIENTS,

TO PIAN STIEHL COMPANY INC 01' NORTH CHICAGO, ILLINOIS, A CORPORATION OF Application filed my I1,

- To all whom it may concern: I

Be it known that I. CARL A- PFANIS'ITEHL,

' a citizen of the United States, residing in Waukegan, in the county of Lake and State of Illinois, have invented certain new and useful Improvements in Processes for Cleaning Contact-Points, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specifica- .tionw My invention relates to a process for cleaning contact points,,more particularly contact points having contact faces or surhigh temperatures and does not readily, OXlfaces of tungsten and the object of my inventionis to remove from the tungsten contact point the metal which accumulates thereon during the process of mounting the tungsten contact pomt as willbe more fully hereinafter explained. Y

Metallic tungsten is one of the group of nace, and

so called rare metals. It fuses at extremel dize or corrode in ordinary atmosphere. It is extremely hard and therefore can not be cut or worked with ordinary erties are such as .to ma e it admirab adapted for electrical contact points of electrical, switching mechanisms of various types but the hi h cost of the maternal itself 1 together with t e difficulties in working it into shape. .for'use has in the pastpractically prevented its ap lication as a, materlal from which to make e ectrical contact points. v In constructing an electrical contact pomt of the class mentioned I preferably cut from a tungsten rod of the proper diameter'a disk of tungsten of suitable thickness. This disk of tungsten is subsequently fused or weld d upon abase metalbackmg, such for example as steel or iron, by interpos'ing an extremely thin disk or film of copper be tween thetun ten disk and its associated base metal batting and then subjecting the .tungsten disk, backing copper filmfor disk' to the extremelyhigh temperature produced within asuitable elecr nace, itmay tric furnace. While this invention'is not particularly concerned. with the mechanism 50' .a rod' or with the etails of the electric fur-' be well'atthis point to say, that for cutting the tungsten disk from the'end of during the fusing or welding operation an atmosphere of h tained Within .t e

e ectric furnace to pre tools. Its prop In practice the copper disk'l) 1s in a suitable and intermediate droigen is preferably mainvent oxidization of the base metal backing and copper disk or film. I find that duri the fusing or welding operation just mentloned a considerable portion of the copper interposed between the t ten disk and its associated base metal bacfing will flow out over the cylindrical surface ofthc tungsten disk. It is necessary ,in' or(ler to provide a. satisfactory contact. pomt to remove the copper from the surface- -of the tungsten disk. It is the object of to i my present invention to remove this copper Fi 2 is a the wing or weldi completed ,and after t e excess copper has been removed from the tungsten disk b imfirove'd process hereinafter descri bev quite expensive I is-made to the'acview of the same parts after 7 operation has'been I y eferring first to Fig. ,1 at'A I have illustrated a tungsten'disk and at B I have shown L i a base, metal backing provided with an integral shank G.' It will be' understood that the shank C maybe passed'through a suitlever and there riveted to in operative position; Intel-posed between disk'A and the backingB is air-extremely thin-diskor film D, preferably of copper.

14/2/1000 or 2/100Q-of an'inch in thickness.

able aperture in a contact spring or switchretainthe backing B and parts carried thereby "the tungstenv Pre ly a 5 Afterthe several partshave been assemj bled as illustrated in Fig. Lthey are placed 'peratu're within-the furnace'is raised toa point considerabl of the copper. T e tungsten disk A is thus fused or welded to the base metal bac r a I find that during the fusing .or wel operation a considerable rtion of the co or inter osed between h: .disk A. and tge acking flows out of bacln'ng and disk and covers the cylindrical surface of the tungsten disk A'. ,In practice I find that the film of copper remainin between the tungsten disk Aand the but the space between the electric furnace and the tem' f above the fusingpoint 10o 1/1000 of an inch, that portion of the copper flowing from between the tungsten disk be removed to earthen-ware,

A- and the backing B covering the cylindric'al surface of the .contact. As before stated it is necessary that this excess copper provide a satisfactory contact point.

In accordance with my present invention I provide a shallow dish, preferably of and within this shallow earthen-ware dish I place a layer of welded contact points. I then place this dish upon a plate kept cool by means of running water and then cover the contact oints with concentrated nitric acid mixe with a small quantity of heavy parafiin oil. The paraflin oil which is very thick and sluggish has a very high surface tension. Be oreadding the solution of concentrated nitric acid and -paraflin oil to the contact points it is advisable to stir the solution inasmuch as the oil and nitric acid tend somewhat to separate when permitted to stand indefinitely; As will presently be made apparent it is de sirable that the nitric acid when added to the contact points have a very highjsurface tension. If the acid is kept extremely cool by means of running water its surface 'tens'ion is materially increased. An inert thick substance such as heavy paraflin oil materially increases the surface tension .ofthe nitric acid.

I find it desirable to leave the contact points in the mixture of nitric acid and paraflin oil for approximately ten or fifteen minutes,-although noharm is done if the points are left in this mixture for a considerably longer period. The reason for this is that-t and the-base metal backing there will be no circulation of acid within thisspace. The acid which comes into contact with the cop-' per disk between the backing and the tung- -sten disk becomes-spent and no acid works its way into the space mentioned to continue the chemical disintegration of the copper.

- weak caustic solution.

In Fig. 2 I have illustrated how .the acid eats into the copper disk but a slight distance. It will be understood that if it were notfor the high surface tension of the acid to the action of which the contact points are subjected the acid would eat its way rapidly into the space between the tungsten disk and its base metal support and thus detach the tungsten from its support.

After the contact points have been permitted to remain in the acid solution for approximately ten or fifteen minutes the solution is poured off and the contacts are dipped in a weak caustic solution, such for example as caustic soda or caustic potash.

The oints are then rinsed in clear water and ied. I find that if the points are washed in water before being rinsed in the caustic solution there is a tendency to acidulate the water and the weak solution of nitric acid having an extremely low surface tension will work its way into the space between the tunglsten disk and its associated.

us dissolve the copper film.

1. The process of cleaning contacts of the class described which consists in' subjecting the contacts to the attack of a viscous acid solution, rinsing the contacts in a weak caustlc solution and rinsing the contacts in water.

2; The process of cleaning contacts of the class described which consists in subjecting the contacts to the attack of a viscous acid solution and then rinsing the contacts in a weak caustic solution.

3. The process of cleaning contacts of the 1 class described which consists in subjecting the contacts to the action of a solution of I concentrated nitric acid and-'paraflin oil and then I'IIISIIIg the contacts thus treated in a In witness whereof I "hereunto subscribe my name this 8th dayof-July, A. D. 1914.

CARL a PFANSTIEHL.

I Witnesses! .AnsmGAmmm ..MAn rA.Coo1i. 

